High input signal voltages (e.g., 40V −60V) to integrated circuit devices such as graphics processing units (GPUs) are becoming more common because these higher voltages enable power delivery in an efficient manner. Input signals at these levels require high-ratio point-of-load converters which can be small enough to fit on an integrated circuit device. Various high-ratio converters are known, such as switched tank converters (STCs) and transformer-based DC-DC converters, where DC refers to direct current.
A switched tank converter includes capacitors and inductors to convert energy from one voltage level to another. FIG. 1 shows an example of a switched tank converter 100 having a 4:1 conversion ratio (Vout=Vin/4). The tank circuit portion of the switched tank converter is designed to have a resonant frequency close to the switching frequency. Switching losses are reduced by implementing zero current switching.
A transformer-based high-step-down-ratio converter utilizes a transformer to achieve a high-step-down-ratio. A full-bridge circuit or half-bridge circuit is used to invert a DC input signal voltage into a switching waveform. At the transformer secondary winding, either a full bridge circuit or a center-tapped transformer may be used to achieve synchronous rectification, as shown in the transformer-based converter 200 of FIG. 2. The conversion ratio that is provided is equal to the transformer turns ratio of N:1 (Vout=Vin/N).
Drawbacks are associated with both of the approaches described. A switched tank converter requires many components to achieve a high conversion ratio. For example, if the conversion ratio is increased to 6:1, then another stage must be added. Such an additional stage further increases the circuit component count.
With regards to a transformer-based converter, the size of the transformer increases with an increase in the turns ratio to achieve the desired conversion ratio. This results in an increase in the circuit area as well as in core losses in the transformer. Core losses are proportional to the volume of the transformer.